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7. Enzymes — Biochemistry MCQs
KEMU · 81 MCQs with clinical pearls · Prof Jariya
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Sections in this kemu
- Cofactors and Coenzymes — 16 MCQs
- Enzyme Inhibition Clinical — 14 MCQs
- Enzyme Classification — 10 MCQs
- Serum Enzymes in Diagnosis — 8 MCQs
- Enzyme Kinetics — 8 MCQs
- Cardiac Biomarkers — 6 MCQs
- Enzyme Inhibition — 4 MCQs
- Enzyme Regulation — 4 MCQs
- Clinical Enzymology and Isoenzymes — 4 MCQs
- Enzyme Fundamentals — 4 MCQs
- Regulatory Enzymes — 3 MCQs
Sample MCQs with clinical pearls
During glycolysis, glucose-6-phosphate is converted to fructose-6-phosphate without addition or removal of atoms. Which class of enzyme catalyses this reaction?
A) EC1 Oxidoreductases
B) EC2 Transferases
C) EC3 Hydrolases
D) EC4 Lyases
E) EC5 Isomerases ✔
PHOSPHOGLUCOSE ISOMERASE = ISOMERASE (EC5). Rearranges bond structure without adding or removing atoms. Types: MUTASES (move phosphate between atoms), RACEMASES (interconvert D and L forms), EPIMERASES (interconvert epimers). Glucose-6-phosphate → fructose-6-phosphate = aldose → ketose conversion. No net change in molecular formula.\
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During fatty acid activation before beta-oxidation, a fatty acid is joined to coenzyme A using energy from ATP hydrolysis. Which class of enzyme catalyses this bond formation?
A) EC1 Oxidoreductases
B) EC2 Transferases
C) EC3 Hydrolases
D) EC4 Lyases
E) EC6 Ligases ✔
FATTY ACYL CoA SYNTHETASE = LIGASE (EC6). Synthesises C-S bond COUPLED TO ATP HYDROLYSIS. EC6 types: CARBOXYLASES (biotin-dependent, add CO₂ — pyruvate carboxylase, ACC), SYNTHETASES (ATP-requiring — fatty acyl CoA synthetase), AMINOACYL-tRNA SYNTHETASES. Ligases differ from SYNTHASES (EC4) which do NOT require ATP.\
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Luciferase catalyses the oxidation of luciferin in the presence of oxygen and ATP, enabling fireflies to emit light. Luciferase belongs to which of the following enzyme classes?
A) EC1 Oxidoreductases ✔
B) EC2 Transferases
C) EC3 Hydrolases
D) EC4 Lyases
E) EC5 Isomerases
LUCIFERASE = OXIDOREDUCTASE (EC1) — specifically a monooxygenase. Catalyses: luciferin + O₂ + ATP → oxyluciferin + CO₂ + AMP + PPi + LIGHT. O₂ reduced, luciferin oxidised = oxidoreductase. Used in reporter gene assays in molecular biology. The excited-state oxyluciferin releases energy as light upon returning to ground state.\
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81 MCQs are arranged to the learning outcomes of this kemu.
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